1. Field of the Invention
The present invention relates to a method and an apparatus for forming a monomolecular film or a built-up monomolecular film. Specifically, the present invention relates to a method of forming a monomolecular film or a built-up monomolecular film which includes a process of removing a remaining portion of a monomolecular film on a water surface after that portion has been stored in a specific region, and to an apparatus for carrying out such a method.
2. Related Background Art
A conventional method of forming a Langmuir-Blodgett (hereinafter abbreviated to "LB") film comprises spreading a material for forming a monomolecular film onto a water surface, two-dimensionally compressing the material on the water surface, thereby preparing a monomolecular film on the water surface, and transferring the monomolecular film onto a solid substrate (by dipping the substrate through the monomolecular film covered surface). Since a water tank, a constituent of the apparatus being used in the LB film formation, is of a certain limited size, a monomolecular film which can be prepared on the surface of the water contained in the water tank has a correspondingly limited area. This means that, as the depositing process is repeated, and portions of the monomolecular film are deposited one after another onto the solid substrate, the area available for the part of the film remaining on the water surface decreases until the area is too small for the remaining portion of the film to be deposited. Therefore, in order for any further deposition to be carried out, the remainder of the monomolecular film remaining on the water surface has to be removed, and a new monomolecular film has to be prepared there. Thus, the conventional LB film formation employs non-continuous processing in which a process of forming a monomolecular film and a process of removing a remainder of the monomolecular film are alternately performed. In order to overcome this problem, continuous film formation methods and apparatuses for carrying out such methods have been recently proposed (for example, by A. Barraud and M. Vandevyver, in "Thin Solid Films" Vol. 99, page 221, 1983; by W. Nitsch and C. Kurthen, in "Thin Solid Films" Vol 178, page 145, 1989; and by O. Albrecht et al. in "Molecular Electronics" edited by F. T. Hong, page 41, Plenum Press NY, 1989).
However, in practice, the continuous methods which have been proposed have the following problems:
A remainder of a monomolecular film on the water surface is removed with an aspirator. When a continuous film forming method, such as above, is employed, since a plurality of remainders of monomolecular films which remain undeposited are continually generated, as a result of the film forming process, one after another on the water surface, it is necessary to remove the remainders with an aspirator in a successive or periodical manner. Further, since removal of film remainder(s) causes a part of the water contained in the tank to be simultaneously removed, it is necessary to add fresh water to the remaining water in the tank in order to maintain the water level. Since the portion of the water which has been removed contains relatively large amounts of impurities, it cannot be readily used again. This makes it necessary to use, at a great expense, a large amount of water to properly fill the water tank. When the water tank must also contain metal ions, etc., an additional expense is incurred. The additional substance, such as metal ions, may be harmful, and the drainage resulting from the removal of parts of water has to be processed, thereby resulting in further expense. This expense increases proportionally with the increase in the amount of water removed. Another problem arising from the removal of film remainder(s) is that such a removal causes an additional flow of water in the water tank, and this flow of water may adversely influence the deposition of a monomolecular film on the water surface onto the substrate.